1. Field of the Invention
The present invention relates to a multi-point distance-measuring apparatus capable of performing distance measurements in a plurality of directions within a field in a viewfinder and, more particularly, to a multi-point distance-measuring apparatus capable of performing distance measurements at a central portion of a field in a viewfinder with priority.
2. Related Background Art
Many conventional "center distance measurement" type distance-measuring apparatuses wherein a distance between the camera and an object observed within a narrow distance-measuring zone defined at a central portion of a field in a viewfinder have been used in conventional auto focus (AF) cameras. In the "center distance measurement" type apparatus, the distance-measuring zone is limited to only the central portion of the field. Therefore, a principal object falling outside the central portion of the field often tends to be out of focus. In order to eliminate the drawback of this conventional apparatus, the following conventional distance-measuring apparatuses are available:
(1) a multi-point distance-measuring apparatus in which a plurality of positions within a field of view are sequentially set at the center of the field, and an intermediate distance between the longest distance and the shortest distance is calculated to set a lens position (Japanese Patent Laid-Open (Kokai) No. 56-101128);
(2) a multi-point distance-measuring apparatus in which object positions corresponding to a plurality of points set in the field of view are sequentially scanned with a light spot to time-serially detect distances to these points, thereby setting a lens position on the basis of the detected shortest distance (Japanese Patent Laid-Open (Kokai) No. 59-143914); and
(3) a multi-point distance-measuring apparatus in which narrow-field distance measurement for measuring a narrow area within the field and wide-field distance measurement for performing average distance measurement of a wide field are arbitrarily switched upon operation of a selection button in accordance with an object position within the field (Japanese Patent Laid-Open (Kokai) No. 62-14015).
However, the above known conventional apparatuses are arranged such that distance measurements are performed by always projecting light in a plurality of directions even if a principal object is located at the center of the field of view of the viewfinder. It therefore takes a long period of time to measure a distance to an object as compared with a conventional distance-measuring system which has been most popular. In addition, power consumption of a battery is undesirably increased.
More specifically, in each apparatus disclosed in Japanese Patent Laid-Open (Kokai) Nos. 56-101128 and 59-143914, even if a principal object is located at the center of the field of view in the viewfinder, light is always projected in a plurality of directions to measure a distance to the object. Therefore, the power consumption of the battery is increased, and distance-measuring time is also prolonged. In the conventional apparatus disclosed in Japanese Patent Laid-Open No. 62-14015, operations are complicated, and light is projected in a wide range even if an object requires only a narrow-view distance measurement. As a result, the power consumption of the battery is undesirably increased.